Production of hydrogen from packaging wastes by two-stage pyrolysis

Plastic waste continues to increasingly pollute the environment. Currently, a significant portion of this waste is either landfilled or incinerated to generate energy, which leads to substantial CO₂ emissions. However, thermochemical processing is a potential solution to create a circular economy, with pyrolysis combined with the subsequent high-temperature treatment of the vapour-gas mixture being a method preferable to incineration. This study investigated the optimal conditions for the two-stage pyrolysis of non-recyclable plastic waste. The process involved a low-temperature treatment of feedstock, followed by high-temperature exposure of the vapour-gas mixture in the presence of a carbon matrix. The final products of the two-stage pyrolysis were: synthesis gas, mainly consisting of hydrogen and carbon monoxide; solid pyrolysis residue obtained in the first stage and high-carbon material during the second stage was obtained. The first stage of the two-stage pyrolysis was carried out at various temperatures, ranging from 460 to 540 °C, followed by cracking at 600 to 1000 °C, with different ratios of packaging waste to wood charcoal (1:2, 1:4, 1:6). The conditions for obtaining more than 70 vol% hydrogen in the synthesis gas from packaging waste were determined, the effect of changing the process parameters was studied. The decomposition kinetics of packaging waste showed activation energies of the first and second steps: 165 and 255 kJ/mol (Ozawa-Flynn-Wall method), 164 and 259 kJ/mol (Kissinger-Akahira-Sunose method), respectively. This work contributes to the study of efficient recycling methods for non-recyclable packaging waste and promotes advancements in sustainable waste management practices.